Despite a good deal of speculation about the organization and maturation of the neural substrate underlying cross-modal (multisensory) processes, there has been little empirical evidence to support or contradict speculations derived from behavior and introspection. However, using the superior colliculus (SC) neuron, a robust neural model has been developed. In the last funding period we found that the remarkable ability of SC neurons to integrate their cross-modal inputs is not an inborn characteristic, but develops only gradually, and depends on a series of interrelated events. One of the most important of these is the maturation of influences from extraprimary sensory cortex; primarily the anterior ectosylvian sulcus (AES), and less so from the neighboring rostral lateral suprasylvian sulcus (rLS). When these corticotectal influences become functional, SC neurons are rendered capable of integrating cross-modal information, and of mediating multisensory orientation behaviors. Yet, little is known about their development.The present proposal is an attempt to examine this issue. Of specific interest is understanding the normal maturation of synergies among the modality-specific influences from these cortices that make SC multisensory integration possible, and the likely compensatory changes initiated by early damage to AES. But, preliminary observations also provide strong indications that early experience is essential for SC neurons to develop the ability to synthesize their inputs, and it seems likely that these experiences are relayed to it from AES and rLS. Understanding the normal maturation of the neural processes underlying this capacity, whether these processes can be crafted by the external conditions in which they must function, and brain's ability to compensate for damage to critical parts of the circuit, are essential steps in elaborating strategies to deal with developmental anomalies and early traumas that can compromise the normal integrative capabilities of the brain and the perceptions and behaviors that depend on them.